The DOE recomends R-38 in attics. This is 12", unsettled of
cellulose insulation. This would make a great impact on your heating
cost. Are our walls insulated? Cellulose blown into the wall cavities
can also make a large difference.
You may want to have a energy specialists come out to your house and
do a energy audit. This could include a blower door diagnostic, which
will show air leakage into your home. They may also use an infrared
camera to determined if there is insulation in the walls.